fluid transfer system and method

ABSTRACT

The present invention relates to a fluid transfer system and method for transferring fluid from a reservoir ( 2 ) and to (a) delivery device typically being (a) nozzle. The present invention relates in particular to transferring urea in highly accurate metered amounts from a reservoir ( 2 ) to a nozzle ( 5 ) arranged within an exhaust system ( 4 ) of a combustion engine ( 1 ) or combustion engines.

The present invention relates to a fluid transfer system and method fortransferring fluid from a reservoir and to delivery device typicallybeing nozzle. The present invention relates in particular totransferring urea in highly accurate metered amounts from a reservoir toa nozzle arranged within an exhaust system of a combustion engine orcombustion engines.

INTRODUCTION TO THE INVENTION

It has been found that introduction of urea into the exhaust gassesstreaming from an combustion engine and into a catalytic system maydramatically increase the efficiency of the catalytic element'scapability to convert NOx gasses. While urea in it self is relativelyharmless to the environment and the amounts introduced into thecombustion system thereby can be overdosed, such wasting of urea isoften undesirably as the technology is often applied to moving vehiclesand such waste would require larger storage capacities than what isactually needed if urea is dosed correctly.

A need for introducing the required amount of urea into the exhaustgasses only is therefore present. Furthermore, urea is most efficientlyintroduced into the exhaust gasses as a spray of droplet which typicallyrequires that the urea is pressurised and fed to a nozzle.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a fluid transfersystem and method providing an efficient controllable delivery of fluidfrom a reservoir to a nozzle. Thus, in a first aspect the presentinvention preferably relates to a fluid transfer system for transferringfluid from a reservoir to a receiving device, preferably being a nozzle,the fluid transfer system comprising

-   -   a through flow device adapted to receive fluid from the        reservoir and transfer fluid through the system and/or measuring        the amount of fluid being transferred from the reservoir to the        receiving device,    -   a controllable shut-off valve arranged upstream of the receiving        device and preferably downstream of the through flow device,    -   a controlling unit controlling at least the state of the        shut-off valve        wherein the controlling unit is adapted to control the state of        the shut-off valve    -   so that the pressure of fluid being fed to the receiving device        is above a first pre-selected pressure limit (P_(min)), and/or    -   so that the delivered amount corresponds to a demand.

The through flow device may preferably comprise or is a dosing pump, apump, a measuring unit, a measuring pump, or a combination thereof.

In the present context a number of terms are used. Even though these areused in their ordinary meaning, a further exemplary explanation is givenon some of the terms.

Dynamical error in delivered amount: A dynamical error occurs when thedemand for delivered fluid varies with time and is caused by a delaybetween when the amount is delivered an when it should have beendelivered. The delay is typically due to elasticity in the fluiddelivery system, delay in prosecution of controlling and/or sensingsignal and/or the like. A dynamical error may be defined as the maximumvalue of the difference between the desired amount and the actualdelivered amount during a pre-defined time. The dynamical error is notaccumulated.

Accumulative error in delivered amount: An accumulative error indelivered amount is typically defined as an error which is not balancedover time.

Dosing pump: A unit delivering a precise amount of liquid controlled byan electrical signal from a control unit and which is capable of doingso against a high pressure.

Pump (p pump): A unit delivering an uncontrolled flow of liquid againsta high pressure or a unit capable of maintaining a high pressure.

Measuring unit: A unit giving information (most often as electricalsignals) about flow of liquid without influencing flow or pressure.

Measuring pump: A combination of a pump and the measuring unit.

Through flow device: A device adapted to receive fluid from a reservoirand transfer the fluid and/or measuring the amount of fluid beingtransferred from the reservoir and to a receiving device.

Demand: The amount to be delivered. Demand may be the immediate demandexpressed in e.g. liter per hour [l/h] or demand accumulated over aninterval expressed in e.g hour [h].

Delivery: The amount to be delivered. Delivery may be the immediatedelivery expressed in e.g. liter per hour [l/h] or delivery accumulatedover an interval expressed in e.g hour [h].

The invention involves preferably at least two ways of dosing fluid(further ways are explained later on). The first one may be summarisedin the following manner:

1. Use of a dosing pump: In such embodiments, the dosing pump providesvery accurately the amount demanded and the dosing pump is accordinglycontrolled to provide a delivery corresponding to a demand. Thepressurisation of the fluid is preferably obtained by a combination of afluid buffer arranged downstream of the dosing pump and a shut-off valvearranged downstream of the buffer.

The second one is based on using a measuring unit. In such embodiments,the fluid is pressurised in some manner; typically the fluid is storedpressurised in a reservoir or pressurised by a pump. A demand istypically expressed at regular intervals and the total amount to bedelivered in a given interval is typically estimated to equal the demand(in l/h) at the beginning of the interval multiplied with the length (inhour) of the interval. Use of a dosing unit may be summarised in thefollowing manner:

2a: The delivery of fluid can be estimated from a functionalrelationship giving delivered amount per hour multiplied by the openingtime of the shut-off valve. From such a relationship the time in a giveninterval the valve must be open for meeting a demand. During deliverythe actual delivered amount is measured by the measuring unit, and ifdiscrepancy is found between the estimated delivered amount and theactual delivered amount a feed back is made to the algorithm determiningthe opening time of the shut-off valve to take into account thediscrepancy.

2b: The actual delivery is measured during delivery. Once the demand ina given interval has been met, the shut-off valve is closed.

It should be noted that the above summaries are examples only, thatvariations of these two occurs and they are therefore not intended to beconstrued in a narrowing way. However, they are believed to provide anindication on a framework for the present invention. For instance, insome embodiments according to the present invention, the measuring unitand pressurisation unit are integrated into each other.

As it will appear in the following, a pump will in some embodimentpressurise fluid received from the tank. However, in some otherembodiment the system receives pressurised fluid from the tank and insuch embodiment the pump will not be necessary.

The present invention relates in a second aspect preferably to a methodof transferring fluid from a reservoir to a receiving device, preferablybeing a nozzle, the fluid transfer system comprising

-   -   a through flow device adapted to receive fluid from the        reservoir and transfer fluid through the system and/or measuring        the amount of fluid being transferred from the reservoir to the        receiving device,    -   a controllable shut-off valve (9) arranged upstream of the        receiving device and preferably downstream of the through flow        device,    -   a controlling unit controlling at least the state of the        shut-off valve        the method comprising controlling the state of the state of the        shut-off valve    -   so that the pressure of fluid being fed to the receiving device        is above a first pre-selected pressure limit (P_(min)), and/or    -   so that the delivered amount corresponds to a demand.

Also in this connection the through flow device may preferably compriseor is a dosing pump, a pump, a measuring unit, measuring pump or acombination thereof.

The controlling of the shut-off valve to meet a given demand ispreferably performed based on direct control of the shut-off valve basedon the system characteristic for obtaining a minimum dynamic error and acorrection signal from the measuring unit to modify an algorithm forcontrolling the valve in order to avoid accumulative error.

The present invention and in particular preferred embodiments thereofwill now be described in details with reference to the accompanyingfigures, wherein

FIG. 1 shows schematically a combustion system according to a preferredembodiment of the present invention,

FIG. 2 shows schematically a first embodiment of a fluid transfer systemunit according to the present invention,

FIG. 3 shows schematically three different flow regimes obtainable bythe fluid transfer systems according to the present invention,

FIG. 4 shows a second embodiment of the invention in a conceptual manner

FIG. 5 shows the a variant of the system in FIG. 4 where thepressurising and measuring function is combined,

FIG. 6 shows schematically an embodiment of a fluid transfer systemaccording to the present invention corresponding to FIG. 4,

FIG. 7 shows schematically an embodiment of a fluid transfer systemaccording to the present invention corresponding to FIG. 5,

FIG. 8 shows schematically another embodiment of a fluid transfer systemaccording to the present invention corresponding to FIG. 5,

FIG. 9 shows schematically a third embodiment of a fluid transfer systemaccording to the present invention corresponding to FIG. 5,

FIG. 10 shows graphically an example on a strategy for delivery of ureaaccording to preferred embodiments of the present invention,

FIG. 11 shows graphically details on a strategy for delivery of ureaaccording to preferred embodiments of the present invention, and

FIGS. 12 and 13 each show schematically preferred embodiments ofmeasuring units according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a combustion system comprising a combustion engine 1,typically being a Diesel engine, a tank 2 holding a liquid solution ofurea (also known under the trade name AdBlue) and a catalytic system 3.The exhaust of the engine 1 is connected to the catalytic system 3 by anexhaust pipe 4. The combustion system further comprising a nozzle 5connected to a fluid transfer unit 6 (broadly termed “a through flowdevice”) which is connected to the tank 2. The fluid transfer unit 6receives the liquid solution of urea and provides it to the nozzle 5 inamounts meeting the demand for urea in the catalytic system at least tosome extend.

FIG. 2 shows schematically the architecture of the fluid transfer unit(6 in FIG. 1) for introducing urea into the exhaust system of acombustion engine. Same numerals as used for designating elements inFIG. 1 are used for designating similar elements in FIG. 2. The systemarchitecture as shown in FIG. 2 comprises a dosing pump 7 connected atits inlet to the tank 2 for pumping and dosing urea to a buffer 8. Thebuffer 8 is via a shut-off valve 9 connected to the nozzle 5.

The dosing pump 7, of the embodiment according to FIG. 2, is a pumppressurising fluid and generating a controllable variable flow rate andthereby a controlled delivery. This means that the actual flow rate canbe controlled very precisely. The accuracy of the flow rate delivered bythe dosing pump 7 is typically lower than +/−1% of the full-scaledelivery when the delivery is larger than 10% of the full-scaledelivery. Below that amount, the accuracy is lower than +/−10% of thereading value being the amount the dosing pump 7 is set to provide. Thedosing pump is controlled by a motor control unit 11 which receivesinput representing the actual demand for urea and the motor control unit11 sets the dosing pump to pump this actual demand.

In order to render the different functions of the system of FIG. 2 morevisible, the motor control unit 11 and the shut-off valve control unit10 is shown as different elements of the system. However, those twounits may be assembled into a single unit. Basically, the two unitsserves the following two purposes:

Motor control unit 11, which on the basis of parameters defining thestate of the engine e.g. load and rpm defines the actual demand for ureaand signals the demand to the dosing pump 7. The dosing pump 7 may be anordinary dosing pump measuring an amount of urea meeting the actualdemand for urea and pressurise the metered amount of urea to a pressurelevel being sufficient for the nozzle to provide atomisation of themetered urea.

Shut-off valve control unit 10 controlling the state of the shut-offvalve i.e. changes the shut-off valve state from open to close or viceversa on the basis of the pressure of the fluid measured in the buffer 8and at the same time provides a desired distribution of the periods inwhich the shut-off valve is open.

All parts of the system may be integrated into a single unit. However,the tank and the nozzle are typically not integrated parts of thesystem, whereby the system may be placed at an appropriated place ofe.g. a truck. The nozzle 5 is a nozzle that provides atomized fluid oncethe pressure of the fluid fed to the nozzle 5 is above a thresholdP_(max). Above that threshold the amount of fluid being atomized equalsthe amount of fluid provided by the dosing pump 7. However, below thethreshold, the nozzle 5 will not be able to atomize all fluid, as theamount of fluid streaming towards the nozzle is too small to build up apressure above the threshold. When this occurs, the shut-off valve 9controls whether fluid is fed to the nozzle 5 or not in the mannerdisclosed below. In typical applications the amount of fluid to beatomized ranges from e.g. 0.1% to 100% of the maximum amount of fluid tobe atomized and atomization of a continuous flowing fluid over such aninterval is typically not considered feasible.

The shut-off valve 9 is a valve that opens when the pressure in thefluid pumped towards it is above a maximum pressure limit P_(max) (FIG.3) and closes once the pressure is below a minimum limit P_(min).P_(max) is typically 5% higher than P_(min) and P_(min) is the level atwhich it can be assured that the fluid fed to the nozzle 5 is atomizedby the nozzle 5. Below that pressure level, the nozzle 5 may be able toatomize but it can in general not be assured, as atomization requires apressure difference across the nozzle of a certain level. Thus, when theflow rate from the dosing pump 7 is to small to provide a pressure aboveP_(min), the shut-off valve closes and stays closed until the dosingpump 7 has pumped sufficient fluid to build up a pressure above P_(max).Once the pressure exceeds P_(max) the shut-off valve 9 opens and thefluid streams through the nozzle 5. During this streaming the amountbeing atomised is higher than what is delivered by the dosing pump 7 sothe pressure drops until P_(min) where the valve closes and a pressurebuild up is initiated again. By this procedure, the amount of fluidatomised in time average equal to the amount of fluid delivered by thedosing pump 7.

Referring to FIG. 3, this figure shows three different atomisationregimes, large flow (FIG. 3 a) medium flow (FIG. 3 b) and small flow(FIG. 3 c). As shown in FIG. 3 a the instantaneous pressure in the flowmeasured at the inlet of the shut-off valve 9 is after a whileconstantly above the limits of P_(max) and P_(min). If the demanddecreases, the amount of fluid pumped by the dosing pump 7 will decreaseresulting in a pressure decrease. The pressure can be decreased untilP_(min) and stay constant at a level above P_(min) as long as thedecrease occurs from a level being above P_(max). If the demand is verylarge or e.g. the nozzle 5 is clogged, the pressure may increase untilit reaches a safety limit P_(high) at which the dosing pump 7 stopspumping fluid but the shut-off valve 9 stays open.

When the demand for atomized fluid is at medium flow the atomisationenters into the regime disclosed schematically in FIG. 3 b. In thisregime, the pressure measured at the inlet of the shut-off valve 9 is atone instance lower than P_(max) and the shut-off valve 9 is accordinglyclosed; it is here assumed that the shut-off has not been opened, i.e.the state is reached from a level where the shut-off valve has beenclosed. As the shut-off valve 9 is closed and the dosing pump 7 is stillpumping, fluid will be accumulated in the buffer 8 and as the buffer 8is a resilient member accumulation of fluid therein will take placeresulting in that the pressure at the inlet of the shut-off valve 9 willincrease. This pressure increase will continue as long as the dosingpump 7 is pumping and the shut-off valve 9 stays closed. Once thepressure reaches P_(max) the shut-off valve 9 will open. Opening of theshut-off valve 9 will result in that fluid is streaming towards thenozzle 5. The fluid streaming towards the shut-off valve 9 is acombination of fluid being pumped by the dosing pump 7 and the change involume of the buffer 8. The effect of the decreasing buffer volume isindicated in FIG. 3 b with the dotted line denoted “pressure dropwithout inflow”. The amount of fluid pumped by the dosing pump 7 is, inthe regime shown in FIG. 3 b, insufficient to keep the pressure aboveP_(min), and once the pressure has dropped to P_(min) the shut-off valve9 closes where after accumulation of fluid in the buffer 8 begins,again, with an increasing pressure as a result. This cycle continues aslong as the demand for fluid is not changed. As it appears, the flowthrough the nozzle 5 in this regime will be pulsed and the time lengthof each pulse is the time from opening of the shut-off valve at P_(max)until closing of the shut-off valve at P_(min)

A minimum flow regime is schematically shown in FIG. 3 c. As shown inFIG. 3 c the pressure does not reach the limit of P_(max) being thepressure at which the shut-off valve 9 open for fluid flowing to thenozzle 5. In order to atomize fluid, the shut-off valve 9 is forced openat intervals, typically being at regular intervals. The time where theshut-off valve 9 is closed is in FIG. 3 c indicated by “set timeinterval” and the length thereof is pre-selected as the maximumallowable time for no delivery. The time length of a pulse is in FIG. 3c is indicated as “pulse time”. A cycle in this minimum flow regimecomprises two phases. The first phase begins (for instance) when thepressure is at P_(min) and the shut-off valve 9 closes. As the dosingpump 7 continues pumping the pressure increases as disclosed above inthe medium flow regime. When the set time interval has passed theshut-off valve 9 is forced open and as the fluid flows towards and outof the nozzle 5, the pressure decreases until the pressure reachesP_(min). By utilising this forced opening of the shut-off valve the timeintervals between two pulses can be kept lower than if one should awaita pressure build-up to P_(max) and as the intervals between two pulsescan be kept low one may be able to provide e.g. an even delivery of ureain the streaming exhaust gasses. The length of the time interval betweentwo pulses is typically pre-selected and is typically found byperforming experiments.

The various flow regimes, high, medium and minimum, are defined byselecting P_(max) and P_(min) in combination with selecting the lengthof “set time interval”. Actual values of these parameters are selectedin accordance with an actual nozzle configuration. In a typicalembodiment, P_(max) is selected to be 8.4 bar, P_(min) is selected to be8.1 bar and “set time interval” is selected to be one or a few seconds.In such embodiments, the minimum amount of fluid being fed to the nozzle5 is around 0.010 l/h, the flexibility of the buffer 8 is 160 mm³/bar.

The opening and closing of the shut-off valve 9 is electromagneticallycontrolled from a valve controlling unit 10 as shown in FIG. 2 by theconnection 12. The connection 12 transfers an electrical signal to theshut-off valve 9.

The buffer 8 may provide the effect that the frequency at which theshut-off valve 9 operates can be decreased compared to a system where nobuffer 8 is incorporated in the system.

When the shut-off valve 9 is closed and the dosing pump 7 pumps fluidthe pressure within the fluid transfer system increases. The fluid isconsidered to be incompressible and once the shut-off valve 9 is openedthe pressure in the fluid transfer system will, if no buffer 8 isincorporated and the dosing pump 7 is not pumping, drop to the leveloutside the nozzle 5 almost instantaneously. However, as the buffer 8 isa resilient member the contraction of the buffer's 8 volume willmaintain the pressure within the fluid transfer higher than P_(min) fora much longer period, thus the time between two consecutive openings ofshut-off valve 9 can be of sufficient length to secure a sufficient lifetime of the shut-off valve 9. Besides improving the valve life timeexpectancy the buffer will make it possible to use a much slower (andthus cheaper) valve. If the buffer is too big it can introduce anunacceptable dynamic error.

A pressure sensor 13 measures the pressure within the buffer 8. Themeasured pressure is used for controlling the state of the shut-offvalve 9 (open or close) and the pressure measured is used as if it wasthe pressure measured at the inlet of the valve. The measured pressureis signalled to a controlling unit 10 via the connection 14. Theconnection 15 from the shut-off valve 9 to the nozzle 5 is sufficientlystiff to assure that once the shut-off valve 9 is opened the pressureincrease in the connection 15 will in a substantial manner not result inany deformation of the connection 15. If, on the other hand, theconnection was not substantially stiff, opening of the shut-off valve 9would cause the connection 15 to expand resulting in that the amount ofurea streaming out of the outlet of the shut-off valve 9 would notsubstantial instantaneously equal the amount streaming out of the nozzle5 which normally would be considered as introducing errors into thefluid transfer system. In order to provide suitable stiffness, theconnection 15 is typically a line made of stainless steel. The stiffnessof the connection 15 helps also to minimize droplets from being formedat the outlet of the nozzle as the shutting-off of the shut-off valve ifdone sufficiently fast will result in that no fluid will stream out ofthe nozzle. If, on the other hand, the connection 15 was notsufficiently stiff the connection would contract once the shut-off valveis shut-off resulting in fluid being forced out of the nozzle and adroplet formed at outlet of the nozzle. Such droplet may crystallise andresult in clogging of the nozzle. It is noted that such stiff connectionmay be applied to all the embodiments of the invention.

FIG. 4 shows a second embodiment of the invention in a conceptualmanner. In contrast to the first embodiment where the dosing pump'sdelivery substantially equals the actual demand and the pressurisationis made by a combination of accumulating fluid in a buffer and a valve,the system of FIG. 4 is supplied with liquid at a constant pressure(within limits regardless of flow) from a pump 7 or alternatively from apressurised tank 18. Measuring unit 19 providing information on thedelivered amount measures the actual amount delivered. A motor/valvecontrol unit 20 operates the shut-off valve 9 typically and preferablypulsating in a PWM (pulse width modulated) manner in accordance with theactual need for urea in relation to system specific parameters such asnozzle constant, characteristics of the valve, pressure of the fluidbefore the nozzle etc. In this way a change in flow as demanded from themotor conditions will very quickly be provided through the nozzle 5 thusgiving a very little dynamic error. Signals via the connection 21 frommeasuring unit 19 will provide information for changing the PWM ofshut-off valve 9 in order to minimize the accumulative error.

FIG. 5 shows a variant of the system in FIG. 4 where the measuring unitand pump are combined into a single unit 22.

In the following figures (6, 7, 8, and 9) different embodiments forpumping and measuring functions corresponding to FIG. 4 and FIG. 5 areshown. All the embodiments have among other potentials the potential toprovide a fast response (a small dynamic error) and a high accuracy (asmall accumulative error).

FIG. 6 shows an embodiment of the system corresponding to FIG. 4. Inthis embodiment the transfer system comprises a tank 18 containingpressurised fluid. Alternatively, the tank 2 may contain fluid atambient pressure and a pump 17 may provide pressurisation. At the outletof the tank 18 or the pump 17 a valve 23 is provided having its outletconnected to a measuring unit. The measuring unit comprises a piston 24attached to and acting on a membrane 25. As indicated in FIG. 6 themovement of the piston 24 and thus the membrane 25 is limited relativelyto the housing to which it is attached. The piston 24 is biased towardsthe membrane 25 by a spring 26. At the outlet of the measuring unit ashut-off valve 9 is provided which in dosing conditions acts asexplained above with respect to FIG. 4. In non-dosing conditions (whenpiston 24 is moved backwards and liquid is streaming into the measuringunit) the shut-off valve 9 must be closed. The valves 9 and 23 are bothmagnetic valves. Once the shut-off valve 9 is closed and the valve 23 isopened and the force from the fluid flowing through valve 23 and actingon the membrane is larger than the force on the piston 24 coming fromthe spring 26, the spring 26 will be compressed and the piston 24 willbe displaced until stopped by the facing of the house. This end positionis detected of the sensor 27 which through the connection 21 will signalto the control unit which in turn closes the valve 23 and startoperating shut-off valve 9. During this operation the biasing force fromthe spring 26 will displace the piston 24 in opposite direction therebypressing fluid being accumulated in the measuring unit towards theshut-off valve 9.

The fluid transfer system of FIG. 6 is used in the following manner.Initially, the shut-off valve 9 is closed and the valve 23 is opened.Once the valve 23 is opened the membrane 25 and the piston 24 movesagainst the biasing force from the spring 26. The valve 23 stays openuntil the displacement sensor 27 detects that the piston 24 has reachedits bottom position where no further compression of the spring 26occurs. The sensor sends a signal to the control unit 20 once the pistonhas reached its bottom position. Thereafter the valve 23 is closed andthe shut-off valve 9 is opened and operated in PWM mode until the pistonhas reached its top position. The sensor 27 signals this to the controlunit 20. As the displacement of the piston 24 corresponds to a deliveredamount of urea the delivered amount can be monitored by logging thesignal representing the upper or lower most position of the piston 24.Once the piston 24 reaches its upper most position, the shut-off valve 9is closed, the valve 23 is opened and the cycle is repeated. Also thisembodiment may be assembled into a unit as disclosed in connection withthe above embodiment.

FIG. 7 shows an embodiment of the system corresponding to FIG. 5. Inthis embodiment a combined pump/measuring unit performs thepressurisation of the fluid and gives information to the control unit 20about the amount delivered. Again, the transfer system comprising a tank2 connected to the pumping/measuring unit 22 via a valve 23. However, inthis embodiment, the valve 23 is a one-way valve and a further one-wayvalve 28 is arranged in the outlet of the pump/measuring unit. Thepumping in this embodiment also comprises a piston 24, a membrane 25 anda spring 26. The assembly of the piston 24, the membrane 25 and thespring 26 is slidable attached to a sub-piston 29. The sub-piston 29 isconnected via a connecting rod 30 to a crank 31 so that the rotation ofthe crank 31 results in a reciprocating displacement of the sub-piston29. The piston 24 will tend to follow this reciprocating displacement ofthe sub-piston 29. However, as the piston 24 is slidable arranged in thesub-piston 29 and biased by the spring 26 the displacement of the piston24 will differ from the displacement of the sub-piston 29.

Also in this embodiment, the transfer system is equipped with a sensor27 sensing the end positions in the relative movement between piston 24and sub-piston 29. A further sensor 32 is arranged for sensing the upperdead position of the crank 31. When the sub-piston 29 is moved towardsit lower position, the piston 24 will once the spring 26 is fullyexpanded follow this displacement. This will result in that the pressureabove the membrane 25 is decreased causing the valve 23 to open and thevalve 28 to close, thereby fluid will be drawn from the tank and intothe pump/measuring unit. When the sub-piston 29 thereafter moves towardsit upper position the valve 23 closes. During this displacement of thesub-piston 29, the spring will be compressed as the shut-off valve 9 isclosed during this movement and the force from the pressure on themembrane 25 is larger than the force applied by the spring 26 on thepiston 24. When the spring 26 has been maximally compressed and thecrank 31 is stopped in upper dead position (signalled by the sensor 32to the control unit 20) the nozzle can atomize urea in PWM mode aspreviously described and the spring 26 will start to expand. Suchexpansion of the spring 26 will result in that fluid may still bepressurised and delivered even though the crank 31 is not rotating. Infact it may be essential for the function of the system that theshut-off valve 9 only is operated when the crank 31 and thus thesub-piston is not moving.

FIG. 8 shows another embodiment of the system corresponding to FIG. 5.This embodiment has many similarities with the embodiment shown in FIG.7 and same numerals are used for similar elements. As in FIG. 6 themovement of the piston 24 and thus the membrane 25 is limited relativelyto the housing and not relatively to the sub-piston 29 whereby theprecision can be improved and the detection of end positions can besimplified. As shown in FIG. 8 the sub-piston 29 engages with the piston24 via a preloaded spring 33. In the top dead position there is aclearance between spring 33 and sub-piston 29 and in the lower deadposition the spring 33 can be slightly further compressed. This meansthat the movement of the crank mechanism is uncritical concerningprecision. Apart from this the function is as described in connection toFIG. 7.

FIG. 9 shows another embodiment of the system corresponding to FIG. 5.This embodiment comprises a pump/measuring unit connected at the inletto a tank via a one-way valve 23 and at the outlet of thepumping/measuring unit a one-way valve 28 is arranged. The two one-wayvalves 23 and 28 play the same role as the two one-way valves in anormal pump. The pump/measuring unit comprises a piston 24 and amembrane 25 similar to the piston and membrane of the above discussedembodiments. The piston 24 in this embodiment is directly connected to acrank 31 via a connecting rod 30.

The pump is typically controlled to maintain a substantially constantpressure at the shut-off valve 9. The shut-off valve 9 is typicallyopened and closed in a pulsating (PWM) manner based on the actual needfor urea. Due to the highly defined geometry each revolution of thecrank represents a well defined and known volume delivered, and a sensor32 may detect the amount pumped by picking up a signal for eachrevolution or a known fraction of a revolution. This detection isuncritical as an error is not accumulating. The signals will via theconnection 34 provide information for changing the PWM of shut-off valve9 in order to minimize the accumulative error.

The shut-off valve 9 can be operated without interruption in the earlierdescribed manner (PWM).

It should be noted the pump may have two membranes operating in oppositephases, one membrane having a suction stroke, while the other ispumping.

In the above a number of different embodiments are disclosed which eachdeals with delivery of liquefied Urea into an exhaust system. A commoncharacteristic of the different embodiments is the presence of ashut-off valve 9 arranged before the nozzle. Although the shut-off valvemay be dispensed with it is preferably applied in order to control theflow of urea to the nozzle; in some embodiments the shut-off valve is incombination with a buffer used to secure sufficient pressure of thefluid and in other embodiments used to control the amount of fluiddelivered to the nozzle. A combination thereof is, of course, alsopossible.

As indicated, delivery of urea according to the present invention maymainly be performed in four different manners:

I. Open loop operation: From the knowledge of system parameters (such asnozzle constant, pressure of the fluid before the nozzle, temperatureand viscosity of the fluid, characteristics of the shut-off valve etc.)the delivery of urea to the nozzle according to the need demanded(demand) from the motor control unit is controlled according to anadministering algorithm determining opening and closing periods for thevalve. The valve is operated solely on basis of system parameters (e.g.on basis of temperature and pressure measurements) without any feedbackfrom actually delivered volume. Typically, such an operation results ina high cost system.

II. Use of a dosing pump as shown FIGS. 2 and 3. The dosing pumpprovides a highly accurate flow rate and pressurisation is provided by acombination of a buffer and an administering valve; in FIG. 2 theadministering valve is termed shut-off valve.

III. Use of a measuring pump maintaining an approximately constantpressure being high enough to ensure atomization. The measuring pumppressurises the fluid and signals to a motor control unit that a welldefined amount of urea has been delivered. This is indicated in FIG. 5in which the measuring pump is referenced with numeral 22.

IV. Use of a measuring unit as shown in FIG. 4. Use of a measuring unitis especially advantageous in situations where urea is to be added atseveral locations and/or where easy access to pressurisation (e.g.pressurised air) is present. Various embodiments of measuring units aredepicted in FIGS. 12 and 13. Operation of the administering valve may bedone in a similar manner as when a measuring pump is used (FIG. 10).

FIG. 10 shows graphically an example of a strategy for delivery of ureaaccording to preferred embodiments of the present invention. Thestrategy is based on PWM (pulse width modulation). Although PWM and PIM(pulse interval modulation) may both be applied in connection with thepresent invention, it has been found that due to the large dynamic spanof delivery (more than a factor 100 between the largest and smallestdelivery amount per time unit) PIM seems to be less useable due to afixed pulse width, as the width of the pulses must be small in order todeliver small amounts without very large pulse intervals resulting inthat the shut-off valve at larger delivery has to be activates manytimes which in turn results in lower lifetime for the valve.

PWM provides the possibility to choose a suitable pulse interval whiletaking into account the dynamics (typically the buffer effect) of thecatalytic system.

The strategy shown in FIG. 10 is based on comparing accumulated deliverywith accumulated demand at certain points in time (when the measuringpump or the measuring unit send information about delivered amounts tothe motor/valve control unit). Based on this information the algorithmfor controlling the width of the pulses is changed in order to maintaina good accuracy.

In FIG. 10 C0, C1, C2, C3, C4 and C5 represent points in time whereaccumulated delivery is compared with accumulated demand. The immediatedemand (ml/s, labelled demand in FIG. 10) is prescribed by a controllingunit, typically a motor controlling unit. The accumulated demand (ml),delivered amount (ml/s, labelled delivery (pulses)) and accumulateddelivery (ml) are indicated in FIG. 10. Accumulated values maypreferably be determined by integration. For illustration theaccumulated curves are showed as continuous curves but in praxis thecontrol unit will compare values at interval (C1, C2, . . . etc.) andcalculate a single deviation value for use in the next interval (as willbe seen in FIG. 11).

The administrating algorithm determining activation of the shut-offvalve (pulse width) may comprise a number of elements, such asdeviations in the accumulated delivery from accumulated demand, error inaccumulated delivered amount between two feed back times, the rate ofchange at which such error changes etc.

With reference to FIG. 10 delivery is made with a constant pulse withineach interval if the demand is constant. At C1, the accumulated deliveryis compared to the accumulated demand and it is found that the deliveryhas been too high. Consequently, the pulse width is decreased at C1 andkept constant from C1 to C2. At C2 the accumulated demand is againcompared to the accumulated delivery and it is found that theaccumulated delivery still is higher than the accumulated demandalthough the accumulated delivery is approaching the accumulated demand.Consequently, the pulse width is decreased further. Between C2 and C3the demand for delivery is increased and as the accumulated demand ishigher than the accumulated delivery at C3, the pulse width isconsequently increased in order to increase the delivery. At C4 it isfound that the increase is not sufficient to meet the demand and at C4the pulse width is again increased. A more realistic situation withvarying demand and thus varying pulse width within an interval is shownin FIG. 11. Here is shown a single interval Cn−Cn+1 with the same linelabelling as in FIG. 10. Pulse width is determined of the motor/valvecontrol unit as a function of system parameters (nozzle constant,pressure of the fluid at the shut-up valve, viscosity of the fluid,valve characteristic etc.) the need of delivery flow at the start of apulse and the time distance between pulses. The value will beapproximately Fdemand/Fmax*Tp, where Fdemand denotes the need ofdelivery flow at the start of a pulse, Fmax stands for the flow with anopen shut-up valve and Tp is the time between two subsequent pulses.When the volume V(control) has been delivered from the measuring pump(at time Cn+1) the correcting signal is sent to the motor/valve controlunit and the accumulated demand is compared to V(control). The surplus(V(control)−V(Cn−1−Cn)) and the known accumulated error at Cn (ΔCn)determines the accumulated error at time Cn+1.

Obviously there exist a number of strategies to modify the algorithm forpulse width in the following interval. A simple one is aiming to deliverthe accumulated demand volume for the next interval (that meansΔCn+1=ΔCn+2) by multiplying the pulse width function by a factor(ΔCn−ΔCn+1)/V(control). Of course it will never be absolutely correct asthe demand is varying but as this variation is continuous and intervalsare rather short it will give a serviceable approximation. Anotherstrategy will be to aim to have zero accumulative error (ΔCn+2=0).

Embodiments which advantageously can be used in connection with theabove strategy are shown in FIGS. 12 and 13. FIG. 12 shows a measuringunit 19 shaped as a corbie-stepped piston device. However, theembodiments of FIGS. 12 and 13 are applicable in connection with otherstrategies.

The measuring unit 19 comprising a cylinder 39 in which a corbie-steppedpiston 38 is slideable arranged. The corbie-stepped shape of the piston38 is provided by the piston part 38 c whereby the area 38 a is largerthan the area 38 b as shown in the figure. The measuring device 19receives fluid through valve 36. The fluid is pressurised to a pressureP and is received from pressurised reservoir or a pump. The outlet ofvalve 36 connected to the larger displacement volume 40 a of cylinder39, and connected to the smaller displacement volume 40 b of thecylinder 39 via a valve 37. The connection between the valve 37 and thesmaller displacement volume 40 b also comprises a discharge 41 in theconfiguration shown in FIG. 12.

Above the end of the piston part 38 c opposite the end connected to thepiston 38 a displacement volume 42 is provided. This displacement volume42 receives fluid at the same or substantial same pressure P as fed tothe valve 36. In a preferred embodiment, the fluid supplied to valve 36and displacement volume 42 comes from the same source.

FIG. 12 shows two modes of the measuring device. In the upper part ofFIG. 12, valve 36 is open and valve 37 is closed whereby fluid atpressure P streams towards the larger displacement volume 40 a. As thearea of the top of the piston part 38 c is smaller than the area 38 aand the pressure in displacement volumes 40 a and 42 are equal, thepiston 38 will be displaced to the right with reference to FIG. 12. Theright-going movement results in that fluid present in displacementvolume 40 b is pressed out through the discharge 41. This actioncontinues until the piston 38 reaches its right-most position at whichposition valve 36 is closed and 37 is opened; this situation isdisclosed in lower part of FIG. 12. When valve 36 is closed and valve 37is open, the pressure in displacement volume 42 will push the piston 38to the left with reference to FIG. 12. Fluid present in displacementvolume 40 a will flow out, through the valve 37 and into thedisplacement volume 40 b as well as out through the discharge 41. Thisleft-going action continues until the piston 38 reaches its left-mostposition, when the states of the valves 36 and 37 are both changed andthe cycle repeats.

The embodiment of FIG. 12 has among other advantages that the deliveryis present except at the left-most and right-most positions of thepiston and that the pressure of the fluid delivered to the discharge 41is well defined. Furthermore, a strong geometrical relationship ispresent between the amount of fluid delivered through discharge 41 andthe movement of the piston part 38 c.

The size of the areas 38 a and 38 b may be selected so that the sameamount delivered to the discharge irrespective of the way the piston 38moves. This may be achieved when the size of area 38 a is twice the sizeof area 38 b. Furthermore, the sizes of the displacement volumes havethe following ratio 2:1:1 (40 a:40 b:42). Embodiments like the one shownin FIG. 12 has the further advantages that the direction change of thepiston 38 can be performed very quickly and thereby only littleinterruption in fluid delivery is present (the directional change istypically governed by the speed at which the state of the valves can bechanged). In other embodiments where a suction stroke is present theinterruption is comparable larger.

By arranging the valves 36 and 37 as indicated on FIG. 12 redirectionvalves are not needed and the relatively simpler shut-off valves may beapplied.

FIG. 13 shows an embodiment similar to the embodiment of FIG. 12.Features of the embodiment shown in FIG. 13 which are similar tofeatures shown in FIG. 12 have been labelled with the same numerals.Similarly, the upper part of FIG. 12 shows a situation where the piston38 moves to the right, and the lower part shows a situation where thepiston moves to the left.

In the embodiment of FIG. 13, sealing membranes 43 a and 43 b areprovided between the piston 38 and the displacement volume 40 a andbetween the piston part 38 c and the displacement volume 42. Thepresence of the sealing membranes 43 a and 43 b provides a sealhindering fluid from flowing between the volumes 40 a and 40 b pass theedge of the piston 38.

Even though, the present description has focused on differentembodiments each having distinct features it should be emphasised thatfeatures disclosed in connection with one embodiment is applicable inconnection with another embodiment.

1. A fluid transfer system for transferring fluid from a reservoir (2)to a receiving device, preferably being a nozzle (5), the fluid transfersystem comprising a through flow device (6) adapted to receive fluidfrom the reservoir (2) and transfer fluid through the system and/ormeasuring the amount of fluid being transferred from the reservoir tothe receiving device, a controllable shut-off valve (9) arrangedupstream of the receiving device and preferably downstream of thethrough flow device (6), a controlling unit controlling at least thestate of the shut-off valve (9) wherein the controlling unit is adaptedto control the state of the shut-off valve so that the pressure of fluidbeing fed to the receiving device is above a first pre-selected pressurelimit (P_(min)), and/or so that the delivered amount corresponds to ademand.
 2. A fluid transfer system according to claim 1, wherein thethrough flow device comprises a dosing pump, a pump, a measuring unit, ameasuring pump or a combination thereof.
 3. A system according to claim1 or 2, wherein the controlling unit turns the shut-off valve (9) intoits open state when the pressure upstream of the shut-off valve (9) isabove a second pre-selected pressure limit (P_(max)).
 4. A systemaccording to any of the preceding claims, wherein the controlling unitturns the shut-off valve (9) into its closed state when the pressureupstream of the valve (9) is decreased to the first pre-selectedpressure limit (P_(min)).
 5. A system according to any of the precedingclaims, wherein the shut-off valve (9) is an electromagnetic valve.
 6. Asystem according to any of preceding claims, further comprising apressure sensor (13) arranged to measure the pressure of the fluid at alocation upstream of the shut-off valve (9).
 7. A system according toany of the preceding claims, wherein the through flow device comprisinga dosing pump comprising a membrane pump and/or a piston pump.
 8. Asystem according to claim 7, wherein transfer system comprising a fluidbuffer (8) arranged upstream of the shut-off valve and downstream of thedosing pump.
 9. A system according to claim 1-6, further comprising avalve (23) arranged upstream of the through flow device.
 10. A systemaccording to claim 9, wherein the through flow device comprising apiston (24) and a membrane (25), the piston is abutting, such asengaging, the membrane (25).
 11. A system according to claim 10, furthercomprising a displacement sensor (27, 32) sensing the displacement ofthe piston (24).
 12. A system according to any of the claims 10 or 11,further comprising a spring (26) being arranged so that the spring (26)is biasing the piston (24) towards the membrane (25).
 13. A systemaccording to any of the claims 10-12, wherein the piston (24) is inslideable engagement with a sub-piston (29) and the sub-piston (29) isconnected to a crank (31) by a connecting rod (30).
 14. A systemaccording to claim 13, further comprising a one-way valve (28) arrangedupstream of the shut-off valve (9) so as to allow fluid to flow towardsthe shut-off valve (9) only and wherein the valve (23) arranged upstreamof the through flow device is a one-way valve allowing fluid to flowtowards the through flow device only.
 15. A system according to any ofthe preceding claims 9-11, wherein the piston (24) is connected to acrank (31) by a connecting rod (30).
 16. A system according to claim 15,further comprising a one-way valve (28) arranged between the throughflow device and the shut-off valve (9), the one-way valve (28) isarranged to allow fluid to flow towards the shut-off valve (9) only. 17.A system according to claim 9, wherein the through flow device comprisesa measuring unit (19) the system comprising a cylinder (39) in which acorbie-stepped piston (38) is slideable arranged, so as to provide twodisplacement volumes (40 a, 40 b) of different sizes and a second valve(37), wherein the inlet of the valve (36) arranged upstream of thethrough flow device is connected to or connectable to a fluid source andthe outlet of said valve (36) being connected to the larger of thedisplacement volumes and to the inlet of the second valve (37), theoutlet of the second valve (37) being connected to the smaller of thedisplacement volumes and to a discharge.
 18. A system according to claim17, wherein the cylinder (39) further comprising a further displacementvolume (42) provided above a piston part (38 c) forming part of thepiston (38), the displacement volume (42) being connected to orconnectable to a fluid source, preferably being the same fluid source towhich the inlet of valve (36) is connected to or connectable to.
 19. Asystem according to claim 17 or 18, wherein the two displacement volumes(40 a, 40 b) is sealed from each other by a membrane (43 a) and whendepending on claim 18, the smaller displacement volume (40 b) is sealedfrom the further displacement volume (42) by a membrane (43 b).
 20. Asystem according to any of the preceding claims, further comprising afluid connection (15) extending from the shut-off valve (9) to thereceiving device, the connection is stiff so as to avoid expansion ofthe connection (15) which would cause uncontrollable flow through theconnection due to contraction of the connection (15) when the shut-offvalve (9) is closed.
 21. A system according to any of the precedingclaims, further comprising the reservoir (2).
 22. A system according toany of the preceding claims, wherein the delivery device is a nozzle(5).
 23. A system according to claim 19, wherein the nozzle (5) isarranged in an exhaust system so that it sprays fluid into the exhaustsystem.
 24. An exhaust system comprising a fluid transfer systemaccording to any of the preceding claims.
 25. A method of transferringfluid from a reservoir (2) to a receiving device, preferably being anozzle (5), the fluid transfer system comprising a through flow device(6) adapted to receive fluid from the reservoir (2) and transfer thefluid through the system and/or measuring the amount of fluid beingtransferred from the reservoir to the receiving device, a controllableshut-off valve (9) arranged upstream of the receiving device andpreferably downstream of the through flow device (6), a controlling unitcontrolling at least the state of the shut-off valve (9) the methodcomprising controlling the state of the state of the shut-off valve sothat the pressure of fluid being fed to the receiving device is above afirst pre-selected pressure limit (P_(min)), and/or so that thedelivered amount corresponds to a demand.
 26. A method according toclaim 25, wherein the through flow device comprises a dosing pump, apumping unit, a measuring unit, as measuring pump or a combinationthereof.
 27. A method according to claim 25 or 26, wherein thecontrolling of the state of the shut-off valve comprising turning theshut-off valve (9) into its open state when the pressure upstream of theshut-off valve (9) is above a second pre-selected pressure limit(P_(max)).
 28. A method according to any of the claims 25-27, whereinthe controlling of the state of the shut-off valve comprising turningthe shut-off valve (9) into its closed state when the pressure upstreamof the valve (9) is decreased to the first pre-selected pressure limit(P_(min)).
 29. A method according to any of claims 26-28, furthercomprising measuring the pressure of the fluid at a location upstream ofthe shut-off valve (9) and downstream of the pump (7).
 30. A methodaccording to any of the claims 25-29, comprising measuring the amountflowing through the through flow device.
 31. A method according to claim30, further comprising turning the state of the valve into it closedstate if the amount measured by the through flow device exceed a demand.32. A method according to any of the preceding claims 25-31, wherein thethrough flow device comprises a dosing pump and wherein the dosing pumpis operated to provide an immediate delivery substantial equal to animmediate demand.
 33. A method according to any of the claims 25-31,wherein the through flow device comprises a measuring unit and whereinthe controlling of the shut-off valve so that the delivered amountcorrespond to a demand comprising operating the shut-off valve inPWM-mode (pulse width modulation-mode).
 34. A method according to claim33, further comprising determining the accumulated demand for a giveninterval, accumulating the delivery during at least part time of theinterval by the measuring unit and adapting the width(s) of one or morepulses in said interval so that the accumulated delivery in saidintervals equals the accumulated demand.
 35. A method according to claim34, wherein the controlling of the shut-off valve comprising closing theshut-off valve once the accumulated delivery has reached the accumulateddemand in said interval.
 36. A method according to any of the claims33-35, wherein the through flow device comprises a measuring unit, themethod comprising A) operating the shut-off valve in PWM-mode with oneor more pulse widths in a time interval, B) at the end of said timeinterval comparing the accumulated delivery with the accumulated demand,C) at the end of said time interval setting the pulse width(s) of thePWM-mode for a succeeding time interval in response to the comparisonand operating the shut-off valve with the so changed pulse width(s) inan succeeding interval, D) repeating steps B) and C).
 37. A methodaccording to claim 36, further comprising setting the pulse width(s)while delivering during said interval.
 38. A method according to claim33-37, wherein setting of the pulse width(s) comprising adjusting anadministering algorithm.
 39. A method according to 36-38 wherein thepulse width(s) are varying during a time interval.
 40. A methodaccording to 36-38 wherein the pulse width(s) are equal during a timeinterval.
 41. A method according to any of the claims 36-40, wherein theaccumulated delivery is the amount delivered since a selected point intime, and the accumulated demand is the amount demanded since theselected point in time,
 42. A method according to claim 41, wherein theselected point in time is an instant where the accumulated demand andaccumulated delivery is reset, such as when the delivery is initiated.43. A method according to any of the preceding claims 41 or 42, whereina selected point in time is at the end of a last selected time period sothat method is performed in a cyclic manner.
 44. A method according toany of the preceding claims 25-43, wherein the fluid is urea or ureaderivatives.
 45. A method according to any of the preceding claims25-44, wherein the reservoir (2) stores pressurised fluid at apre-selected level or comprising such as is a pump pressurising fluid toa pre-selected level.
 46. A method according to any of the claims 25-45,wherein the method is embedded in a system according to any of the claim1-24.